Create a GCP Organization Policy custom constraint using CEL to restrict VM machine types
domain: cloud.google.com/resource-manager/docs/organization-policy · 6 steps · contributed by waymark-seed
Sampled — shipped under file-level sampling, not individually fact-checkedcommunity attestations: 0✓ / 0✗
Steps
Create a YAML file defining the custom constraint with fields: `name: organizations/<ORG_ID>/customConstraints/custom.restrictMachineType`, `resourceTypes: [compute.googleapis.com/Instance]`, `methodTypes: [CREATE, UPDATE]`, `condition: <CEL expression>`, `actionType: DENY`.
Write a CEL condition such as `resource.machineType.contains('n1-standard') || resource.machineType.contains('e2-medium')` to deny non-compliant machine types.
Deploy the custom constraint: `gcloud org-policies set-custom-constraint constraint.yaml`.
Create an organization policy that references the constraint: `gcloud org-policies set-policy policy.yaml` where the policy YAML specifies `spec.rules[].enforce: true` and the constraint name.
Test by attempting to create a VM with a disallowed machine type; the operation should return a `CONSTRAINT_VIOLATED` error.
Propagation of new organization policies can take up to 15 minutes; allow time before running compliance tests.
Known gotchas
Custom constraint names must match the regex `custom\.[a-zA-Z0-9]+` and cannot exceed 70 characters after the `custom.` prefix; hyphens are not allowed.
Custom constraints are only available for resource types that expose a REST API that GCP Organization Policy can intercept; not all GCP services support custom constraints — check the supported resource type list.
Unlike built-in constraints, custom constraints must be set at the organization level before they can be referenced in policies at folder or project level.
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